- Caurinus dectes Russell is a minute, brachypterous scorpionfly
which was discovered at Marys Peak, Benton County, Oregon, in
1976, and subsequently described as the only representative of the
subfamily Caurininae within the Boreidae (snow scorpionflies).
Caurinus dectes is now known to range from the Olympic Peninsula
and Northern Cascades in Washington, to northern Lane County,
The habitats of C. dectes include moist, forested sites with
both coniferous and deciduous canopies. Larvae and adults have
been found in bryophytes occurring as epiphytes, or on logs and
stumps, and in terrestrial stands of mosses and liverworts.
Feeding studies showed that both adults and larvae of Caurinus
are specialized feeders on leafy liverworts (Jungermanniales).
Twenty-five species of Jungermanniales in 15 genera were highly
acceptable to adults, while 11 species in 10 genera were accepted
slightly, if at all. Adults of C. dectes fed to some degree on
two of four genera of the thalloid Metzgeriales, while liverworts
of the Marchantiales and Anthocerotae were not accepted at all.
Larval feeding preferences paralleled those of adults.
The eggs of C. dectes are glued to the leaves of the host
liverworts. Eggs hatch in spring, but some eggs may remain in
diapause for a year or more. Larval feeding is within the shoot
tissues, and is completed within 2 to 3 months of eclosion. There
appear to be 3 larval instars. The fully grown larva constructs
a silk-lined pupal cell within or under the substrate.
The pupal molt occurs between July 1 and August 15, adult
emergence is between September 1 and October 15. The major period
of adult activity extends from eclosion to April. Mating and
oviposition may occur through most of this period. There is
evidence that some fraction of the adult population may perenniate.
The univoltine life cycle, probable perenniation of adults, and
extended egg diapause all are unusual within the Boreidae.
The external morphology of larva and pupa, and internal and
external morphology of adults are described. The larva is
curculioniform, as compared with the scarabaeiform larvae of other
Boreidae; the pupa is decticous and exarate.
The most aberrant structures of adult Caurinus (cf. other
Boreidae), the short rostrum and retractable postabdomen of the
female, are probably adapted to the dorsoventral organization of the
host liverworts. C. dectes is highly specialized, but a number of characters
are primitive with respect to other boreids. These characters
justify the recognition of Caurinus as the sister- group of all
other boreids. Certain characters of C. dectes, including the free
cerci of the female, support the view that the Boreidae are not
closely related to other mecopteran families.